The Mirena coil v. the Pill

The Mirena IUS (intrauterine system) is like many other types of intrauterine contraceptive devices (IUCDs or coils) in that it has to be fitted by a trained doctor and remains in the uterus for a certain amount of time, after which it has to be changed. It consists of a plastic T-shaped frame and the stem of the T has a tiny reservoir containing 52mg of a progesterone hormone called levonorgestrel. Once fitted, about 20 micrograms a day are delivered to the endometrium (lining of the uterus).

Mirena is licensed for five years' use and after this time needs to be removed and replaced. A very small amount of hormone is absorbed into the bloodstream, but much less than the progestogen-only pill (POP), and rarely leads to side effects. If side effects do occur they are transient (four to six weeks) and include headache, breast tenderness and water retention. It contains no oestrogen and therefore has no risks for those women who cannot take the combined Pill.

When is it fitted?
As with all coils the Mirena should be fitted when you are certain you are not pregnant. It is usually done within a week of beginning a period, since this not only reduces the risk of the uterus expelling the coil, but also irregular bleeding, as the endometrium is thin at this time. It can be fitted immediately after termination of pregnancy, but you should wait six weeks after having given birth.

If it is fitted at other times extra contraceptive methods should be used for seven days. Before the Mirena is fitted the doctor will examine you to make sure the pelvic organs are healthy and normal in size. The risk of pelvic infection is slightly raised for three weeks or so after fitting a Mirena, unlike the copper IUCD, where the risk is much higher, mainly in under-25s, who should have a swab taken to exclude chlamydia infection.

When the IUS has been removed, another can be fitted straight away. The lining of the uterus and fertility returns to normal within a month of removal.